This invention relates to additives for synthetic resins and more particularly to additives for thermosetting or thermoplastic synthetic resins containing [polydiene]/[polyester] block copolymers (hereinafter referred to as PD-PES block copolymers).
Although many kinds of thermosetting and thermoplastic synthetic resins are widely used as residential building materials such as for bath tubs and purification tanks, as industrial materials such as for machines and electrical products, as materials for transportation machines such as automobiles and railroad wagons and further as storage tanks and containers, it is a common practice, when they are used for processing, to add other types of synthetic resins, fillers, fiber-reinforcing materials, etc. to improve their physical characteristics such as mechanical strength. It is particularly important to improve their impact strength when their products are used for construction purposes. For this reason, it has been known to blend rubber materials and other polymers in addition to many kinds of reinforcing materials, depending on the purpose for which the material will be used.
It has also been known to blend rubber materials and other thermoplastic synthetic resins in unsaturated polyesters which are examples of thermosetting synthetic resins because their volumes become reduced by 7-10% at the time of molding such that external appearance and accuracy in measurements of their molded products are adversely affected. Among the well known rubber materials which are used for improving impact strength and reducing mold shrinkage as mentioned above, there are polybutadienes, butadiene-styrene copolymers, butadieneacrylnitrile copolymers, butadiene-styrene-acrylonitrile copolymers and modified polybutadienes.
Synthetic resins which are principally used for reinforced plastics with improved impact strength are commonly referred to as matrix resins. As matrix resins, thermosetting unsaturated polyester resins and thermoplastic resins such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyamide, etc. are widely used for such purposes. Reinforced plastics are produced by adding a rubber-type substance, a reinforcing material, a pigment, a filler, etc. to these synthetic resins and applying many kinds of molding processes.
Since matrix resins and rubber materials are so different from each other in physical characteristics such as polarity and solubility parameters, it is extremely difficult to mix them together uniformly or to disperse them stably. Molded products obtained from an unstably mixed thermosetting synthetic resin compound have imperfect surface conditions. Indentations and protrusions are observable and rubber materials may appear on the surface. Desired mechanical strength is not achieved and shrinkage is not reduced. If use is made of an unstably dispersed thermoplastic synthetic resin compound, furthermore, one of the components may coagulate at the time of molding. This affects the molding characteristics adversely and increases the fluctuations in the physical characteristics of molded products.
For reasons stated above, it has been desired to develop additives which can uniformly mix with and stably disperse in thermosetting or thermoplastic matrix resins. They must have good molding characteristics so that products with superior surface qualities can be manufactured, besides being able to improve the mechanical strength of the molded products and to reduce their shrinkage. The present invention therefore relates to additives for synthetic resins which will satisfy these requirements.
Many ideas have been advanced for improving compatibility and/or dispersibility with thermosetting or thermoplastic synthetic resins. For molding the rubber material to be added, graft polymerization of a rubber material with another monomer such as styrene, maleic acid, methacrylates, acrylates, etc. has been considered (for example, Japanese Patent Publications Tokkai No. 54-18862 and 54-40846). Their graft efficiency is not high and their compatibility and dispersibility are not satisfactorily high. For improving compatibility with thermosetting synthetic resins, styrene-type block copolymers have been considered (Japanese Patent Publications Tokkai Nos. 53-74592 and 60-99158). Although compatibility can be improved to a certain extent by them, they are not desirable from the points of view of shrinkage and impact strength since use is made of styrene-type polymers which basically lack strength. Rubber modification of unsaturated polyester resins has also been considered such as the Diels-Alder addition of conjugate diene products such s dicyclo-pentadiene to the double bond of unsaturated polyester containing .alpha., .beta.-unsaturated dicarboxylic acid (Japanese Patent Publication Tokkai No. 58-2315). Although improved compatibility with unsaturated polyester resins can be expected because the amount of conjugate diene-type products which are added is small, it is not effective from the points of view of shrinkage and impact strength.